It is brought in to resist on the other side (8)
I believe the answer is:
opposite
'on the other side' is the definition.
(I've seen this in another clue)
'it is brought in to resist' is the wordplay.
'is brought in to' is an insertion indicator.
'resist' becomes 'oppose' (I've seen this before).
'it' going into 'oppose' is 'OPPOSITE'.
(Other definitions for opposite that I've seen before include "Reverse or antithesis" , "Corresponding" , "antipodean" , "Diametrically contrary" , "Antithetical, vis-a-vis at" .)